An annual calendar mechanism for a watch movement is disclosed in EP Patent No. 0 987 609 in the name of Frédéric Piguet. According to this Patent, the mechanism comprises a date disc provided with thirty one inner teeth located at a first level and to which thirty one figures are affixed, each corresponding to an indication of the day of the month, these figures appearing in succession through an aperture arranged in a dial. A drive wheel set for the date disc comprises a drive wheel that is connected via an intermediate wheel set to the hour wheel of the watch movement. This drive wheel set, fitted with a drive finger, completes one revolution in twenty-four hours and is able to drive the date disc through one step once per day via its inner toothing to control the date display.
The Piguet mechanism further comprises a device for correcting the date indication at the end of each of the months of less than thirty-one days. The date disc therefore comprises a second toothing secured to the date disc and located at a second level. This additional toothing is provided with two juxtaposed teeth spaced from each other by a thirty first of a revolution and drives once a month a wheel which carries a month cam via two intermediate wheels. The month cam is arranged to be actuated at the end of each month by the additional tooth and to make one revolution per year. It carries fine teeth corresponding to the months of less than thirty one days, each of these teeth being arranged to be at the end of the months of less than thirty one days, on the path of the beak of a lever. This lever carries a correction wheel set fitted with a correction finger able to cooperate with the second toothing at the end of the months of less than thirty one days to drive the date disc through an additional step at the end of these months of less than thirty one days when the lever pivots following the passage of its beak over a tooth of the month cam. The correction wheel set is arranged, like the date drive wheel set, to complete one revolution in twenty-four hours.
The mechanism as described has several drawbacks. First of all, the month cam, which includes indications identifying the months of the year and appearing in succession through an aperture pierced in the watch dial, is driven, as has just been seen, by a toothing secured to the date disc. Consequently, it is impossible to correct the month indication without having simultaneously to act on the date mechanism. This can be inconvenient when the watch has, for example, stopped on the 10th day of a given month and when one wishes to reset it to the correct date on the 15th day of the following month. In such case, one would have to scroll down in succession all of the numbers corresponding to the date indications from the “11th”, to the “31st” then from the “1st” to the “15th”.
Moreover, as has also been seen, the device for correcting the date indication at the end of each of the months of less than thirty one days requires a second toothing to be provided on the date disc, provided with two juxtaposed teeth separated from each other by a thirty first of a revolution. The month cam is arranged to be actuated in succession by each of these two teeth by moving forward by one twenty fourth of a revolution each time. If a quick correction device were used, one would not be able to determine which of the two teeth of the second toothing of the date disc was about to actuate the month cam, such that a phase shift would be liable to occur between the date display and the month indication. This quick correction mechanism therefore cannot be employed in the annular calendar mechanism disclosed in the Piguet Patent.
Finally, the Piguet mechanism cannot be used with an instantaneous calendar device. Thus, referring to the Figures of the Piguet Patent, it can be seen that at midnight on the 30th of a month of thirty days, the date ring indicates the 31st. Consequently, during a time period that extends from 21h00 on the “30th” of a month of 30 days and 02h30 on the “1st” day of the month following the month of thirty days, the date indication provided by the watch is incorrect.
It is an object of the present invention to overcome the aforementioned drawbacks in addition to others by providing an annual date mechanism for a watch movement which, in particular, can be corrected simply and quickly.